fixed small bug and two typos, improved performance
fixed small bug and two typos, improved performance

fixed small bug when p == 2 and a couple of typos in documentation; used bitwise left shift operator to improve performance
shivaenigma/pycoin,richardkiss/pycoin,zsulocal/pycoin,mperklin/pycoin,XertroV/pycoin,richardkiss/pycoin,zsulocal/pycoin,mperklin/pycoin,pycoin/pycoin,moocowmoo/pycoin,pycoin/pycoin,XertroV/pycoin,moocowmoo/pycoin,shivaenigma/pycoin